1. Field of the Invention
This invention relates to a fixture for holding a hole-cutting tool having cutting edges to be ground, which fixture comprises a displaceable and/or rotatable baseplate, a stand, which is secured to said baseplate, a bracket, which is carried by said stand, and a gripping unit, which comprises two gripping jaws, which are adapted to grip said tool and are detachably mounted on said bracket in one predetermined position and adapted to be mounted thereon in at least one additional predetermined position. The fixture is intended for use with a grinding unit, which comprises a grinding wheel for grinding a tool when it is gripped by said jaws.
2. Description of the Prior Art
Fixtures for holding twist drills to be ground have been disclosed, e.g., in U.S. Pat. No. 4,270,315 (and the corresponding German Patent Specification 29 15 601) and in U.S. Pat. No. 4,547,999 (and the corresponding German Patent Specification No. 31 46 664). Each of said known fixtures comprises a gripping unit including two prismatic gripping jaws for gripping the drill to be ground. Said gripping unit is pivoted on a horizontal pivot pin, which is adapted to be detachably mounted in different positions on a stand disposed adjacent to the grinding unit. When the twist drill is to be reground by the end face or the peripheral surface of the grinding wheel the gripping unit is to be pivotally urged about the pivot pin against the grinding wheel by hand.
German Patent Specification No. 35 17 034 (published after the Convention date of the present application) and the corresponding U.S. patent application Ser. No. 855,092 now U.S. Pat. No. 4,716,688 disclose such a fixture in which the gripping unit is mounted on an upright mounting pin, which is mounted on the base of an angle bracket, which has a back structure that is pivoted to the stand on a horizontal pivotal axis, which is at right angles to the axis of the mounting pin. That design ensures that the gripping unit will be precisely held in position and need no longer be urged by hand so that even twist drills which are relatively large in diameter can be reground in the workshop in which they have been used. But in that known fixture the back structure has a tapered surface, which is in backlash-free contact with the gripping unit mounted on the mounting pin so that the gripping unit is clamped in position and can be detached by hand only with difficulty. Besides, the twist drill to be ground cannot easily be adjusted.